The following U.S. patents are incorporated herein by reference.
U.S. Pat. No. 4,773,215 discloses a stern drive marine propulsion system that has an inboard engine with an exhaust, an outboard drive unit operatively coupled to the engine and separated therefrom by a transom having two exhaust passages there through, and an exhaust control assembly aft of the engine exhaust and forward of the transom and within the boat. The assembly has an inlet connected to the engine exhaust, and has first and second outlets communicating with the respective exhaust passages extending aft through the transom. A valve in the assembly selectively controls communication of the inlet with the first outlet.
U.S. Pat. No. 4,995,233 discloses a stern drive marine propulsion system having an inboard engine, an outboard drive unit and propeller operatively coupled to the engine and separated therefrom by a transom having two exhaust passages there through. An exhaust control assembly has an inlet connected to the engine exhaust, first and second outlets communicating with respective exhaust passages extending aft through the transom, and a valve in the assembly having a first condition providing communication of the inlet with the first outlet, and a second condition blocking communication of the inlet with the first outlet. Automatic control circuitry automatically controls actuation of the valve between the first and second conditions in response to a given parameter.
U.S. Pat. No. 6,299,496 discloses an exhaust control system for a propulsion system used on a marine vessel. Several parameters are monitored by a controller and the controller uses the information provided by these sensors to control the position of a valve within an exhaust conduit assembly. Sound level is measured at a preselected position on the marine vessel and the degree of opening of the valve is controlled to limit the noise level emanating from the exhaust system. Some exhaust can be diverted directly to the atmosphere through the transom as long as the noise level does not exceed a preselected limit, which can typically be a state law regulation. If a noise level is exceeded, the controller forces the exhaust through an underwater discharge point, typically through the propeller hub of the marine propulsion system.
U.S. Pat. No. 8,876,566 discloses a marine drive and marine exhaust pipe that include a main exhaust flow chamber and an auxiliary idle relief chamber. The auxiliary idle relief chamber vents exhaust above the surface of the body of water in which the vessel is operating.
U.S. Pat. No. 9,376,194 discloses secondary mufflers configured to discharge exhaust gases from an outboard motor to atmosphere surrounding the outboard motor when an internal combustion engine of the outboard motor is operated at idle and at low speeds. The secondary mufflers comprise a housing having an open interior, an inlet port configured to convey the exhaust gases to the open interior, and an outlet port configured to discharge the exhaust gases from the open interior. An exhaust grommet is connected to the outlet port. The exhaust grommet comprises a body that is configured to engage with a cowl of the outboard motor and an extension that extends through the outlet port and protrudes into the open interior. The extension and the body together define a through-bore that is configured to convey the exhaust gases from the open interior to the atmosphere.
U.S. Patent Application Publication No. 2009/0269999 discloses a silencing system for a marine exhaust system that incorporates a single muffler for each engine of the marine vessel. The muffler is provided with two sound dampening chambers interconnected by several exhaust openings between the chambers. A Y-shaped exhaust type system directs exhaust streams from both sides of an engine toward a single exhaust conduit which extends through a transom of the marine vessel. The muffler is provided with a drain opening that allows water to flow out of the first chamber of the muffler in order to maximize the available volume within that chamber for use in sound attenuation. The outlet of the second chamber is provided with a baffle plate that directs the flow of exhaust gas in a forward direction toward the transom of the marine vessel and a deflection surface that directs the exhaust gas to flow in a downward direction toward the surface of the body of water in which the marine vessel is operated.
U.S. patent application Ser. No. 15/174,201, filed Jun. 6, 2016, discloses an intake system for a marine drive. The intake system comprises a throttle device that receives intake air for combustion; an intake conduit that conveys the intake air to the throttle device, wherein the intake conduit has an upstream inlet end, a downstream outlet end, and a radially outer surface that extends from the upstream inlet end to the downstream outlet end; and an intake silencer coupled to the radially outer surface and configured to attenuate sound emanating from the intake system.